Remove Gateway service and configuration

- Delete Gateway module, associated Spring Boot application, and related configuration (`GatewayApplication.java`, `application.yml`, and `pom.xml`).
- Remove Gateway references in `docker-compose.yml`, `.gitlab-ci.yml`, and `backend/pom.xml`.
- Update backend services to directly handle requests under `/api` prefix (e.g., `/api/customers`, `/api/contact`).
- Adjust frontend contact route to connect directly to the server, replacing gateway references with server URLs.

frontend/app/api/contact/route.ts

@@ -3,10 +3,10 @@ import {NextRequest, NextResponse} from 'next/server'
 const HCAPTCHA_SECRET = process.env.HCAPTCHA_SECRET ?? ''
 const SHARED_API_KEY = process.env.SHARED_API_KEY ?? ''
 
-// Detect whether to use localhost or Docker gateway
-const useLocalGatewayEnv = process.env.USE_LOCAL_GATEWAY
-const useLocalGateway = useLocalGatewayEnv?.toLowerCase() === 'true'
-const gatewayHost = useLocalGateway ? 'http://localhost:8080' : 'http://gateway:8080'
+// Detect whether to use localhost or Docker server
+const useLocalServerEnv = process.env.USE_LOCAL_SERVER
+const useLocalServer = useLocalServerEnv?.toLowerCase() === 'true'
+const serverHost = useLocalServer ? 'http://localhost:8080' : 'http://server:8080'
 
 export async function POST(req: NextRequest) {
     try {
@@ -42,7 +42,7 @@ export async function POST(req: NextRequest) {
         // }
 
         // Step 2: Forward to backend service
-        const backendRes = await fetch(`${gatewayHost}/api/contact`, {
+        const backendRes = await fetch(`${serverHost}/api/contact`, {
             method: 'POST',
             headers: {
                 Origin: origin,